Ground fault circuit interrupter (“GFCI”) devices are used to disconnect a circuit when the electric current is not balanced between the energized hot conductor and the neutral return conductor. This current imbalance can be caused by leakage current through an unplanned path to ground. As a safety device for people, a GFCI device quickly disconnects the current source from the circuit to prevent a lethal leakage current through the body of a person who is grounded. By quickly disconnecting the current source from the circuit the GFCI device can mitigate the harm caused by an electric shock.
GFCI devices are typically required by building codes to be integrated with electrical outlets, particularly in areas where an energized circuit may come into contact with people. For example, the U.S. National Electric Codes requires electrical outlets to have GFCI devices for construction sites, bathrooms, kitchens, garages, outdoor areas and near hot tubs or spas. GFCI devices can also be incorporated into electrical appliances that may be considered to pose a particular safety hazard so that protection can be provided even if the connected electrical outlet does not incorporate a GFCI. For example, long extension cords that can be used outdoors, garden equipment, or a hair dryer, could include an in-line GFCI that would minimize the risks of electric shock.
Contemporary GFCI devices are intended to protect people from electric shock by interrupting the circuit if the leakage current exceeds a range of 4-6 mA within 25 ms. A domestic power supply voltage at 50 or 60 Hz alternating current (AC) may induce ventricular fibrillation at currents as low as 60 mA. If there is a direct pathway to the heart or head, a much lower current of less than 1 mA can have a lethal effect. Electricity will always take the path of least resistance, and when this path involves people in water, there is a risk that a contemporary GFCI device's high trip level will not protect people if this path is through the heart or head. Since contemporary GFCI devices interrupt the current source at much higher amperages they may not provide a sufficient safety margin to prevent death in some cases. In addition, the higher trip level of contemporary GFCI devices may be insufficient to protect sensitive electronics or medical devices.
To adequately protect people in a wet environment, such as a hot tub or swimming pool, a GFCI device must trip far below the contemporary GFCI device trip levels of 4-6 mA. There is a need for GFCI devices that detect ultra-low leakage currents for hot tub and pool heaters, especially for units sold directly to the public where the product may not be installed professionally, have GFCI circuits included, or be connected to an outlet without proper grounding.